Transluminal angioplasty, using balloon catheters, has become increasingly popular because it is significantly less traumatic than the open heart surgery required for a coronary bypass operation. In the angioplasty procedure, an elongated catheter having a dilatation balloon or expander member at its distal end is routed through the vascular system to a coronary artery that may be partially occluded with fatty deposits or other types of lesions. Once placed in the desired position, the balloon of the catheter is expanded by a liquid under relatively high pressure to compress the fatty deposit against the walls of the vessel, and force open the occluded artery.
During this procedure, there is a possibility that the balloon may burst or the catheter tube may fail under the relatively high pressure of the inflation liquid. Therefore, the inflation liquid must be carefully selected to avoid catastrophic injury to the patient should such bursting or failure occur, and the liquid is accidentally released into the vessel of the body.
Air and other gases, if present in the catheter, are not quickly absorbed by the blood and are particularly dangerous, with the possibility that an air embolus might be formed. Moreover, if the balloon is inflated with a radiopaque marking fluid, the presence of air may result in error in the accurate positioning of the balloon relative to the occlusion being treated.
Accordingly, it is necessary to purge the air from the catheter prior to use. In the initial stages of the procedure, upon removal of the balloon catheter from its package, these catheters are typically purged of air prior to use so that only the inflation liquid fills the catheter. In accordance with one method of preparing the balloon catheter for use in the body, the balloon and catheter lumen are filled with an inflation liquid, typically a saline solution mixed with radiographic contrast media. The air mixes with the liquid which is then withdrawn from the catheter. Unfortunately, this time consuming procedure must be repeated as many times as necessary to ensure the proper removal of air.
Another technique to purge air from a catheter utilizes catheters that provide a separate tube, which may be removable, that is connected to an opening in the balloon so that air can be forced out through it as the liquid fills the balloon. For an example of this type of catheter, see U.S. Pat. No. 4,684,363 to Ari et al. However, with this type of catheter, air may be reintroduced through the opening of the balloon when the liquid is withdrawn to collapse the balloon before insertion into the patient. The additional tube also creates disadvantages when it is desirable to provide a catheter having a very low profile.
It has also been the practice to purge air from a catheter by creating a vacuum inside the lumen of the catheter, typically in conjunction with a syringe used for liquid filling purposes. Trapped air is withdrawn from the catheter and replaced by the liquid medium which is injected into the lumen of the catheter by the syringe. In such a procedure, air which is purged from the catheter is collected in the syringe. Keeping the syringe in an upright position to permit the air to rise to the plunger of the syringe, the liquid medium is then injected into the catheter to provide inflation of the balloon.
This air purging technique still requires extra time, and involves a number of repeated steps and exercises. Moreover, there is a degree of difficulty in purging air from catheters of smaller sizes, or which have a construction which does not facilitate this air purging technique.
Both the amount of time required and the degree of difficulty in purging the air from a catheter prior to its use have been a problem in the field of angioplasty. The procedures described above are time consuming and require additional equipment to be located in the catheterization laboratory, which may already be crowded with instruments and devices.
Accordingly, there is a need for a balloon tipped catheter having an improved mechanism for purging air from the balloon and catheter lumen.